One common skin test is a scratch test. For this test, a doctor or nurse will scratch
the skin with a tiny bit of liquid extract of an allergen (such as pollen or food).
Allergists usually do skin tests on a person's forearm or back. The allergist then
waits 15 minutes or so to see if reddish, raised spots (called wheals) form, indicating
If the doctor thinks someone might be allergic to more than one thing — or
if it's not clear what's triggering a person's allergy — the allergist will
probably skin test for several different allergens at the same time.
When a skin test shows up as positive with a certain food, that only means a person
mightbe allergic to that food. In these cases, doctors may want
to do additional testing.
To diagnose a food allergy for certain, an allergist might do a blood test in addition
to skin testing. This involves taking a small blood sample to send to a laboratory
for analysis. The lab checks the blood for IgE antibodies to specific foods. If enough
IgE antibodies to a particular food are in the blood, it's very likely that the
person is allergic to it.
If the results of the skin and blood tests are still unclear, though, an allergist
might do something called a food challenge. During this test, the person is given
gradually increasing amounts of the potential food allergen to eat while the doctor
watches for symptoms.
Skin tests may itch for a while. If your child undergoes one, the allergist
might give you an antihistamine or steroid cream for your child to use after
the test to lessen the itching.